1. Field of the Invention
The present invention relates to a stereo matching processing apparatus, a stereo matching processing method, and a computer-readable recording medium. More particularly, the present invention relates to a method for automatically generating three-dimensional data from stereo images.
2. Description of the Related Art
Stereo matching of images acquired from artificial satellites, aircraft, etc. to generate three-dimensional landform data [Digital Surface Model (DSM) data] is widely employed as one method of automatically generating three-dimensional data from stereo images. A stereo matching process is for finding matching points, at which the same position is picked up, from two images or so-called stereo images that are captured from different viewpoints, and calculating the depth to an object of interest or its shape according to the principle of triangulation by using the disparity between the matching points.
Various stereo matching processing techniques have already been proposed. For example, Unexamined Japanese Patent Application KOKAI Publication No. H3-167678 discloses a method that employs an image correlation technique that is widely used. This image correlation technique is a method of finding matching points by setting a correlation window as a template in a left image, calculating a coefficient of intercorrelation between the template and a search window in a right image as their matching degree while moving the search window in the right image, and searching out a position at which the matching degree is high.
This method reduces the amount of processing by restricting the search window to move only in the direction of an epipolar line in the image, and thus can obtain, for each point in the left image, an amount of x-direction displacement, i.e., disparity, of a point in the right image that matches that point in the left image. An epipolar line is a line that, for a given point in one of stereo images, can be drawn in the other of the stereo images as a range in which a point that matches that given point can exist. Epipolar lines are described in “Handbook of Image Analysis” (editorially supervised by Mikio Takagi and Haruhisa Shimoda, published by University of Tokyo Press, January 1991, pp. 597-599).
Normally, the direction of an epipolar line is different from the direction of an image scanning line. However, coordinate transformation can reorient the direction of the epipolar line to be brought in line with the direction of the image scanning line. This coordinate transformation technique is described in “Handbook of Image Analysis” identified above. In a stereo image that is reoriented in the way described above, the matching point search window can be restricted to move only on the scanning line. Therefore, a disparity can be obtained as a difference between the x-coordinate values of the matching points in the left and right images.
Stereo images include a shaded portion (occlusion region) of an object. A matching technique that enables correct matching by not matching any region against this occlusion region by stereo matching is proposed (see Unexamined Japanese Patent Application KOKAI Publication No. H4-299474).
Unexamined Japanese Patent Application KOKAI Publication No. 2002-157576 describes a technique for a stereo image processing apparatus that can automatically generate three-dimensional data of a complicated object from satellite stereo images or aerial stereo images with no presence of an operator. The technique of Patent Literature 3 automatically corrects fault data portions such as noises, omissions, etc. in the three-dimensional data obtained by a stereo processing unit, by using information of outer shapes of buildings, etc. that is retrieved from map data stored in a map data storage unit.
The map data storage unit supplies map data representing outer shapes of buildings, etc. to a DSM data automatic correction unit.